Heat exchangers are commonly used in several technical fields, such as transports, air conditioning, thermal work or fuel cells. Many families also exist if we consider their structure, or the way in which the pipes for transporting the fluids are constructed and positioned. The heat exchangers of which the invention is part comprises plates in which the fluid transport pipes are encased. Such a structure offers the advantages of being compact while maintaining good mechanical resistance, in particular with respect to fluids at high pressure. A recent example is described in the document U.S. Pat. No. 6,467,535 B1, where the plates comprise an external envelope defining a volume which walls, one part with the envelope, divide into flow pipes for the two fluids. Such plates may be made from a single piece by an extrusion process which, conjointly with an adequate thickness of the envelope and the walls, ensures the desired level of resistance.
However, connecting the plate pipes still causes some problems. As the pipes are parallel and adjacent, the channels which take the two fluids to and from the exchanger must be also, alternating on the width of the plate, which creates constraints as assembly is difficult and the channels must also withstand the fluid pressures, whereas it is unlikely that it is possible to construct with the same resistance as the pipes. The connections thus become the weak points of the heat exchanger, and it is not possible to reinforce them.